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.Dd March 13, 2022
.Dt FBIO 4I
.Os
.Sh NAME
.Nm fbio
.Nd frame buffer control operations
.Sh DESCRIPTION
The frame buffers provided with this release support the same general interface
that is defined by
.In sys/fbio.h .
Each responds to an
.Dv FBIOGTYPE
.Xr ioctl 2
request which returns information in a
.Vt fbtype
structure.
.Pp
Each device has an
.\" FBTYPE isn't macro, enum, or type, just used to describe a number of
.\" CPP-macros of the form #define FBTYPE_xxxx
.Sy FBTYPE
which is used by higher-level software to
determine how to perform graphics functions.
Each device is used by opening it, doing an
.Dv FBIOGTYPE
.Xr ioctl 2
to see which frame buffer type is
present, and thereby selecting the appropriate device-management routines.
.Pp
.Dv FBIOGINFO
returns information specific to the GS accelerator.
.Pp
.Dv FBIOSVIDEO
and
.Dv FBIOGVIDEO
are general-purpose
.Xr ioctl 2
requests for controlling possible video features of frame buffers.
These
.Xr ioctl 2
requests either set or return the value of a flags integer.
At this point, only the
.Dv FBVIDEO_ON
option is available, controlled by
.Dv FBIOSVIDEO .
.Dv FBIOGVIDEO
returns the current video state.
.Pp
The
.Dv FBIOSATTR
and
.Dv FBIOGATTR
.Xr ioctl 2
requests allow access to special features of newer frame buffers.
They use the
.Vt fbsattr
and
.Vt fbgattr
structures.
.Pp
Some color frame buffers support the
.Dv FBIOPUTCMAP
and
.Dv FBIOGETCMAP
.Xr ioctl 2
requests, which provide access to the colormap.
They use the
.Vt fbcmap
structure.
.Pp
Also, some framebuffers with multiple colormaps will either encode the colormap
identifier in the high-order bits of the
.Dq index
field in the
.Vt fbcmap
structure, or use the
.Dv FBIOPUTCMAPI
and
.Dv FBIOGETCMAPI
.Xr ioctl 2
requests.
.Pp
.Dv FBIOVERTICAL
is used to wait for the start of the next vertical retrace
period.
.Pp
.Dv FBIOVRTOFFSET
Returns the offset to a read-only
.Dq Em vertical retrace page
for those framebuffers that support it.
This vertical retrace page may be mapped into user space with
.Xr mmap 2 .
The first word of the vertical
retrace page (type
.Vt "unsigned int" )
is a counter that is incremented every time there is a vertical retrace.
The user process can use this counter in a variety of ways.
.Pp
.Dv FBIOMONINFO
returns a
.Vt mon_info
structure which contains information about
the monitor attached to the framebuffer, if available.
.Pp
.Dv FBIOSCURSOR ,
.Dv FBIOGCURSOR ,
.Dv FBIOSCURPOS
and
.Dv FBIOGCURPOS
are used to control the hardware cursor for those framebuffers that have this
feature.
.Dv FBIOGCURMAX
returns the maximum sized cursor supported by the framebuffer.
Attempts to create a cursor larger than this will fail.
.Pp
Finally
.Dv FBIOSDEVINFO
and
.Dv FBIOGDEVINFO
are used to transfer
variable-length, device-specific information into and out of framebuffers.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr mmap 2
.Sh BUGS
The
.Dv FBIOSATTR
and
.Dv FBIOGATTR
.Xr ioctl 2
requests are only
supported by frame buffers which emulate older frame buffer types.
If a frame buffer emulates another frame buffer,
.Dv FBIOGTYPE
returns the emulated type.
To get the real type, use
.Dv FBIOGATTR .
.Pp
The
.Dv FBIOGCURPOS
ioctl was incorrectly defined in previous operating
systems, and older code running in binary compatibility mode may get incorrect
results.
